The present invention relates generally to airplane landing gear assemblies, and more particularly to main landing gear assemblies for large commercial jet airplanes.
Large commercial jet airplanes typically have two main landing gear assemblies swingably attached to the undersides of the wings near the fuselage. The landing gear assemblies are swung downwardly for taxiing and landing of the airplane and are retracted during flight by swinging them inwardly and upwardly into retracted positions wherein the landing wheels are stowed in wheel bays in the airplane fuselage.
Such main landing gear assemblies are subject to two primary mechanical loads during normal operations. When the airplane is stationary or slowly taxiing, the landing gear assemblies are subjected to the downwardly directed static weight load of the airplane. During landing of the airplane, the main landing gear assemblies are additionally subjected to a large, rearwardly directed drag load as the airplane touches down on the runway and the brakes are applied. The drag load is highly dynamic and is imposed in a direction transverse to the weight load, thus generating a highly dynamic moment of force about the points of attachment of the landing gear assemblies to the wings. Ongoing developmental efforts have been directed toward providing a landing gear assembly that can accommodate both the static weight load and the dynamic drag load with a minimum of size and weight.
Main landing gear assemblies presently used in large commercial airplanes generally include a main shock strut swingably attached to the wing structure by a T-shaped trunnion housing at the upper end of the shock strut. The shock strut swings about a trunnion shaft passing through the trunnion housing in a generally forward direction. The trunnion housing turns about the shaft on a pair of trunnion bearings positioned at the opposite ends of the trunnion housing arms. The trunnion bearings are positioned as far out on the arms of the trunnion housing as possible in order that they may have a greater mechanical advantage in bearing the moments of force due to rearward drag loads on the shock strut, and yet also bear the static weight load on the shock strut. With such a configuration, the moment of force about the center of the trunnion housing that arises due to drag loads acts to augment the downward weight load on the rear trunnion bearing and counteract the downward weight load on the forward trunnion bearing.
The shock strut of such a conventionally mounted landing gear assembly is typically braced to withstand drag loads by a pair of diagonal support struts extending from intermediate points on the shock strut cylinder to the outer ends of the trunnion housing arms. Such support struts provide lateral bracing of the shock strut against the rearwardly directed drag load imposed at its lower end during landing. Nevertheless, all weight and drag loads are borne entirely by the two trunnion bearings at the opposite ends of the trunnion housing, thus requiring heavy trunnion bearing assemblies and associated mounting means.
It has been recognized in the past that a net reduction in the total weight of the airplane could be obtained if a portion of the weight and drag loads normally borne entirely by the trunnion bearing assemblies could be borne instead at other fixed points on the body structure. Although any additional supporting structure providing such a function will necessarily add some weight to the landing gear assembly, it has nevertheless been shown that the reduction in size and weight of the trunnion bearing assemblies that would be permitted by such a distribution of the weight and drag loads would more than offset the weight added to the landing gear assembly by the additional support structure.
Specifically, it has been proposed earlier by colleagues of the applicants to construct a landing gear assembly having two additional support struts. Such proposal is the subject matter of the U.S. patent application Ser. No. 107,137 of R. B. Brown and J. A. Stepien, entitled "Body Braced Main Landing Gear," filed concurrently herewith. In accordance with that proposal, a first support strut consists of a rigid strut member pivotably connected at one end to the midsection of the shock strut and pivotably connected at its opposite end to the body structure at a point rearward and inward from the trunnion bearing assemblies. A second strut is pivotably connected to the midsection of the shock strut at one end and is pivotably connected at its opposite end to a fixed point on the body structure at a point forward and inward from the trunnion bearing assemblies. The second strut is further proposed to be foldable by a hinge assembly at its midsection in order to accommodate retraction and extension of the landing gear assembly. The rigid, or nonfolding first support strut functions as a radius rod that necessarily results in fore-and-aft motion of the landing gear during retraction and extension. The main shock strut is proposed to be universally pivotably attached to the trunnion shaft in order to accommodate such fore-and-aft motion, with the result that it is not possible to employ a rigid trunnion integrally formed at the upper end of the main shock strut.
Accordingly, it is an object and purpose of the present invention to provide a main landing gear assembly for an airplane wherein a portion of the weight and drag loads imposed on the landing gear are borne by a pair of support struts attached to fixed points on the wing/body structure inward from the trunnion bearing assemblies. More specifically, it is an object of the present invention to achieve the foregoing object without impairing or altering the normal range of swinging motion of the landing gear along an upright plane during extension and retraction.
It is another object to provide an alternative to the aforementioned proposed landing gear assembly by providing support means for a landing gear assembly which permit retraction and extension of the landing gear by swinging in an upright plane about a rotational axis without substantial fore-and-aft motion.
It is yet another object of the present invention to achieve the foregoing objects and also to provide a landing gear assembly wherein a trunnion housing may be integrally formed in the upper end of the main shock strut.